1. Field of the Invention
The present invention relates to a control apparatus for image blur prevention, which apparatus executes image blur prevention in accordance with an image blur detection output.
2. Related Background Art
The prior arts as objects of the present invention will be described hereinafter.
In current cameras, since all operations such as exposure determination, focusing, and the like, which are important for a photographing operation, are automated, a user, who is not skilled in camera operations, rarely performs unsuccessful photographing operations. However, it is difficult to automatically prevent an unsuccessful photographing operation caused by a camera fluctuation.
In recent years, cameras, which can prevent an unsuccessful photographing operation caused by a camera fluctuation, have been extensively studied. In particular, cameras, which can prevent an unsuccessful photographing operation caused by a hand vibration of a photographer, have been developed and studied.
The hand vibration of a camera in a photographing operation is normally a fluctuation in a frequency range of 1 Hz to 12 Hz. As a basic concept for allowing to take a picture free from an image blur even when such a hand vibration occurs upon releasing of a shutter, a camera fluctuation caused by the hand vibration must be detected, and a correction lens must be displaced in accordance with the detection value. Therefore, in order to take a picture free from an image blur even when a camera fluctuation occurs, first, the camera fluctuation must be precisely detected, and second, a change in optical axis caused by the hand vibration must be corrected.
Detection of the fluctuation (camera fluctuation) can be realized by arranging, in a camera, a fluctuation sensor for detecting an angular acceleration, an angular velocity, an angular displacement, or the like, and a camera fluctuation detection means for outputting an angular displacement by electrically or mechanically integrating an output signal from the sensor. Then, image blur suppression is attained by driving a correction optical mechanism for decentering a photographing optical axis on the basis of the detected information.
A fluctuation prevention system using an angular displacement detection apparatus will be briefly described below with reference to FIG. 27.
FIG. 27 shows a system for suppressing image blurs caused by a camera vertical fluctuation 41p and a camera horizontal fluctuation 41y in the directions of arrows 41 in FIG. 27.
Referring to FIG. 27, the system includes a lens barrel 42, and angular displacement detection means 43p and 43y for respectively detecting a camera vertical fluctuation angular displacement and a camera horizontal fluctuation angular displacement. The angular displacement detection directions of the means 43p and 43y are respectively represented by 44p and 44y. The system also includes a correction optical means 45 (comprising coils 46p and 46y for respectively applying thrusts to the correction optical means 45, and position detection elements 47p and 47y for detecting the positions of the correction optical means 45). The correction optical means 45 has a position control loop (to be described later), and is driven using the outputs from the angular displacement detection means 43p and 43y as target values, thereby assuring stability on an image plane 48.
FIGS. 28 to 31 show the arrangement of an angular displacement detection apparatus as the fluctuation sensor suitable for the above-mentioned object, and the following description will be made with reference to FIGS. 28 to 31.
Referring to FIGS. 28 to 30, components constituting the apparatus are attached to a base plate 51. An outer cylinder 52 has a chamber in which a float 53 and a liquid 54 (to be described below) are sealed. The float 53 is held by a float holding member 55 (to be described later) to be rotatable about a shaft 53a, and a slit-like reflection surface is formed on a projection 53b. The float 53 consists of a material comprising a permanent magnet, and is magnetized in the direction of the shaft 53a. The float 53 is arranged to be rotation-balanced about the shaft 53a, and to be buoyancy-balanced.
The float holding member 55 is fixed to the outer cylinder 52 while holding the float 53 via pivot bearings 56 (to be described later). A U-shaped yoke 57 is attached to the base plate 51, and forms a closed magnetic circuit together with the float 53. A winding coil 514 is arranged between the float 53 and the yoke 57 to have a stationary relationship with the outer cylinder 52. A light-emitting element (IRED) 58 for emitting light upon energization is attached to the base plate 51. A position detection element (PSD) 59 whose output changes depending on the light-receiving position is attached to the base plate 51. The light-emitting element 58 and the position detection element 59 constitute an optical angular displacement detection means of a type for transmitting light via the projection (reflection surface) 53b of the float 53.
A mask 510 is arranged on the front surface of the light-emitting element 58, and has a slit hole 510a which allows light to pass therethrough. A stopper member 511 is attached to the outer cylinder 52 to restrict rotation of the float 53 within a predetermined range.
The above-mentioned float 53 is rotatably held as follows. More specifically, pivot shafts 512 with sharp distal ends are inserted under pressure in the upper and lower central portions of the float 53, as shown in FIG. 29 (A--A section of FIG. 28). The pivot bearings 56 are arranged in the distal end portions of U-shaped upper and lower arms of the float holding member 55 to inwardly oppose each other, and the sharp distal ends of the pivot shafts 512 are fitted in the pivot bearings 56, thereby holding the float.
An upper cover 513 of the outer cylinder 52 is seal-adhered by a known technique using, e.g., a silicone adhesive, to seal the liquid 54 in the outer cylinder 52.
In the above-mentioned arrangement, the float 53 has a symmetrical shape about the rotational shaft 53a so as not to generate a rotation moment due to the influence of gravity at any position, and to exert substantially no load on the pivot shafts. In addition, the float 53 consists of a material having the same specific gravity as that of the liquid 54. In practice, it is impossible to attain an unbalance component=0. However, since only a shape error component corresponding to a specific gravity difference acts as an unbalance component, the unbalance component is substantially very small, and the S/N ratio of friction to inertia is very high, as can be seen from the above description.
In this arrangement, even when the outer cylinder 52 is rotated about the rotational shaft 53a, since the internal liquid 54 stands still by inertia with respect to the absolute space, the float 53 in a floating state is not rotated. Therefore, the outer cylinder 52 is rotated relative to the float 53 about the rotational shaft 53a. The relative angular displacement between the outer cylinder 52 and the float 53 can be detected by the optical detection means using the light-emitting element 58 and the position detection element 59.
Light emitted from the light-emitting element 58 passes through the slit hole 510a of the mask 510, and is radiated onto the float 53. The light is reflected by the slit-like reflection surface of the projection 53b, and then reaches the position detection element 59. Upon transmission of the light, the light is converted into substantially parallel light by the slit hole 510a and the slit-like reflection surface, and an image free from blurring is formed on the position detection element 59.
Since the outer cylinder 52, the light-emitting element 58, and the position detection element 59 are fixed to the base plate 51, and move integrally, if a relative angular displacement motion occurs between the outer cylinder 52 and the float 53, a slit image on the position detection element 59 moves by an amount corresponding to the displacement. Therefore, the output from the position detection element 59 as a photoelectric conversion element, whose output changes depending on the light-receiving position, is proportional to the displacement of the position of the slit image, and the angular displacement of the outer cylinder 52 can be detected on the basis of this output as information.
As described above, the float 53 consists of a permanent magnet material having the same specific gravity as that of the liquid 54, and is prepared as follows, for example.
When a fluorine-based inert liquid is used as the liquid 54, a fine powder of a permanent magnet material (e.g., ferrite) is added as a filler in a plastic material as a base, and its content is adjusted. Thus, it is easy to obtain a specific gravity almost equal to a specific gravity "1.8" of the liquid at the volume content of about 8%. After or simultaneously with molding of the float 53 using the above-mentioned materials, the float 53 is magnetized in the direction of the shaft 53a. Thus, the float 53 can have a nature of a permanent magnet.
FIG. 31 is a sectional view showing the relationship among the float 53, the yoke 57, and the winding coil 514, and taken along a line B--B in FIG. 28.
As shown in FIG. 31, the float 53 is magnetized in the direction of the shaft 53a. In FIG. 31, the upper side of the float 53 is magnetized to have an N pole, and its lower side is magnetized to have an S pole. Lines of magnetic force output from the N pole run into the S pole via the U-shaped yoke 57, thus defining a closed magnetic circuit. When a current is supplied to the winding coil 514 arranged in this magnetic circuit from the back side toward the front side of the plane of the drawing of FIG. 31, the winding coil 514 receives a force in the direction of an arrow f according to the Fleming's left-hand rule. However, the winding coil 514 is fixed to the outer cylinder 52, as described above, and cannot move. Therefore, a force acts in the direction of an arrow F as a reaction, and the float 53 is driven by this force. This force is proportional to the current supplied to the winding coil 514, and the direction of the force is reversed if the current is supplied in a direction opposite to the above-mentioned direction, as a matter of course. More specifically, in the above-mentioned arrangement, the float 53 can be freely driven.
Since a spring force acting on the float 53 by this driving force is a force for maintaining the float 53 at a predetermined position with respect to the outer cylinder 52 (i.e., for integrally moving the float 53) in principle, if this spring force is strong, the outer cylinder 52 and the float 53 move together, and no relative angular displacement for an object angular displacement occurs. However, if the driving force (spring force) is sufficiently smaller than the inertia of the float 53, this arrangement can respond even to an angular displacement at a relatively low frequency.
FIG. 32 is a circuit diagram showing an electrical circuit of the above-mentioned angular displacement detection apparatus.
Current-voltage conversion amplifiers 515a and 515b (and resistors R33 to R36) convert photocurrents 517a and 517b generated in the position detection element 59 by reflected light 516 (originally emitted by the light-emitting element 58) into voltages, and a differential amplifier 518 (and resistors R37 to R40) obtains an output difference between the current-voltage conversion amplifiers 515a and 515b, i.e., an angular displacement (a relative angular displacement motion between the outer cylinder 52 and the float 53). The output from the amplifier 518 is divided by resistors 519a and 519b to obtain a very small output, and this output is input to a driving amplifier 520 (and a resistor R41, and transistors TR11 and TR12), which supplies a current to the winding coil 514 so as to attain negative feedback (the wiring pattern of the winding coil 514 and the magnetization direction of the float 53 are set, so that the float 53 is returned to the center in response to an output from the differential amplifier 518). Thus, as described above, a spring force (driving force) sufficiently smaller than the inertia of the liquid 54 is generated.
An addition amplifier 521 (and resistors R42 to R45) calculates the sum of the outputs from the amplifiers 515a and 515b (the total sum of the light-receiving amounts of the reflected light 516 originally emitted by the light-emitting element 58 and received by the position detection element 59), and supplies its output to a driving amplifier 522 (and resistors R47 and R48, a transistor TR13, and a capacitor C11) for driving the light-emitting element 58.
The light-emitting amount of the light-emitting element 58 changes very unstably in the presence of a temperature difference. However, as described above, when the light-emitting element 58 is driven by the total sum of the light-receiving amounts, the total sum of photocurrents output from the position detection element 59 becomes always constant, and the angular displacement detection sensitivity of the differential amplifier 518 is very stable.
FIG. 33 shows the structure of a servo angular acceleration detection apparatus as another vibration sensor.
Referring to FIG. 33, a support portion 524 is integrally fixed to an outer frame bottom portion 523. Two ends of a shaft 526 are supported by the support portion 524, and bearings 525a and 525b such as ball bearings which suffer less friction. The shaft 526 swingably supports a seesaw 528 to which coils 527a and 527b are attached.
Magnetic circuit boards 530a and 530b as lid portions, and permanent magnets 531a, 531b, 532a, and 532b are arranged above and below the coils 527a and 527b and the seesaw 528 to oppose each other and to be vertically separated from the coils 527a and 527b and the seesaw 528. The magnetic circuit boards 520a and 530b also serve as the lid portions of an outer frame, as described above. The permanent magnets 531a, 531b, 532a, and 532b are mounted on magnetic circuit back plates 533a and 533b fixed to the bottom portion of the outer frame bottom portion 523.
A slit plate 534 formed with a slit 534a which extends in the direction of thickness is arranged on the coil 527a of the seesaw 528. A photoelectric displacement measuring device 535 such as an SPC (separate Photo Diode) is arranged on the magnetic circuit board 530a, which is located above the slit 534a, and also serves as the lid portion of the outer frame, and a light-emitting element 536 such as an infrared light-emitting diode is arranged on the magnetic circuit back plate 533a below the slit 534a.
In the above-mentioned direction, assuming that an angular acceleration a acts on the outer frame in FIG. 33, as indicated by an arrow 537, the seesaw 528 is relatively inclined in a direction opposite to the angular acceleration a, and this fluctuation angle can be detected by the position of the beam emitted from the light-emitting element 536 on the displacement measuring device 535 via the slit 534a.
Magnetic fluxes from the permanent magnets 531a and 531b pass through the permanent magnets 531a and 531b.fwdarw.the coils 527a and 527b.fwdarw.the magnetic circuit boards 530a and 530b.fwdarw.the coils 527a and 527b.fwdarw.the permanent magnets 532a and 532b, and on the other hand, magnetic fluxes from the permanent magnets 532a and 532b pass through the permanent magnets 532a and 532b the magnetic circuit back plates 533a and 533b.fwdarw.the permanent magnets 532a and 532b, thus forming a closed magnetic circuit as a whole, and forming magnetic fluxes in a direction perpendicular to the coils 527a and 527b. When a control current is supplied to the coils 527a and 527b, the seesaw 528 can be moved to the two sides along the fluctuation direction of the angular acceleration a according to the Fleming's rule.
FIG. 34 shows the arrangement of an angular acceleration detection circuit arranged in the servo angular acceleration detection apparatus with the above-mentioned arrangement.
This circuit is constituted by serially connecting a displacement detection amplifier 538 for amplifying the output from the displacement detection device (measuring device) 535, a compensation circuit 539 for stabilizing this feedback circuit system, a driving circuit 540 for further current-amplifying the amplified output from the displacement detection amplifier 538, and energizing the amplified output to the coils 527a and 527b, and the coils 527a and 527b.
In this arrangement, the winding directions of the coils 527a and 527b, and the polarities of the permanent magnets 531a, 531b, 532a, and 532b are set to generate a force in a direction opposite to the fluctuation direction of the seesaw 528 by the external angular acceleration a when the coils 527a and 527b are energized.
The operation principle of the servo angular acceleration detection apparatus with the above-mentioned arrangement will be described below. Assuming that an angular acceleration a externally acts on the angular acceleration sensor with the above arrangement, as shown in FIG. 34, the seesaw 528 fluctuates relative to the outer frame in the opposite rotational direction by the inertia, and hence, the slit 534a provided to the seesaw 528 moves in the direction of an arrow L. For this reason, the center of a light beam radiated from the light-emitting element 536 onto the displacement detection device 535 is displaced, and the displacement detection device 535 generates an output proportional to the displacement amount.
This output is amplified by the displacement detection amplifier 538, as described above, is further current-amplified by the driving circuit 540 via the compensation circuit 539, and is supplied to the coils 537a and 527b.
When a control current is supplied to the coils 527a and 527b, as described above, a force is generated in the seesaw 528 in the direction of an arrow R opposite to the direction of the arrow L of the external angular acceleration a, and an adjusted control current is generated, so that the light beam incident on the displacement detection device 535 is returned to an initial position in a non-application state of the external angular acceleration a.
Note that the value of the control current flowing through the coils 527a and 527b is proportional to the rotational force acting on the seesaw 528, and the rotational force acting on the seesaw 528 is proportional to the force required to return the seesaw 528 to its initial position, i.e., the magnitude of the external angular acceleration a. For this reason, when the current is read as a voltage V via a resistor 541, the magnitude of the angular acceleration a as control information necessary for, e.g., an image blur prevention system of a camera, can be obtained.
The obtained angular acceleration output is second-order-integrated by a known analog or digital integral circuit to obtain a hand vibration output.
FIG. 35 shows in more detail the angular acceleration detection circuit in FIG. 34.
Referring to FIG. 35, an amplifier 538a, and resistors 538b and 538c correspond to the position detection amplifier 538 in FIG. 34, and photoelectrically convert and amplify a photocurrent from the displacement detection device 535 to attain position detection. A capacitor 539a, and resistors 539b and 539c correspond to the compensation circuit 539, and a driving amplifier 540a, transistors 540b and 540c, and resistors 540d, 540e, and 540f correspond to the driving circuit 540 for driving the coils 527a and 527b.
FIG. 36 shows the structure of a vibration gyro as an angular velocity sensor suitable for the above-mentioned object.
The vibration gyro is constituted by a fluctuation mechanism 61, a support mechanism 62 for supporting the fluctuation mechanism 61 with respect to a base, and a control circuit unit 63 connected to the fluctuation mechanism 61.
The fluctuation mechanism 61 is formed by a fluctuation driving portion 64 formed to have a tuning fork shape, and a pair of fluctuation segments 65a and 65b which extend from the distal ends of the fluctuation driving portion 64 so as to weaken the rigidity in a direction perpendicular to the fluctuation surface.
A first piezoelectric conversion element 66 for fluctuation driving and a second piezoelectric conversion element 67 (not shown) for fluctuation driving detection are fixed to the fluctuation driving portion 64. In response to a fluctuation application signal input from the control circuit unit 63 to the first piezoelectric conversion element 66, the fluctuation driving portion 64 and the fluctuation segments 65a and 65b formed integrally with the portion 64 fluctuate in opposite directions, as indicated by arrows 68a and 68b. The second piezoelectric conversion element 67 detects a fluctuation, and outputs it to the control circuit unit 63.
Concentrated mass portions 69a and 69b are respectively formed at the distal end portions of the fluctuation segments 65a and 65b, and have an alternate velocity upon fluctuation of the fluctuation driving portion 64. In this state, when an angular velocity .OMEGA. acts about an axis 610 extending along the fluctuation mechanism 61, Coriolis' forces Fc each defined by a product of the concentrated mass, the alternate velocity, and the input angular velocity act in the directions of arrows 611a and 611b. The reason why the directions of the arrows 611a and 611b are opposite to each other is that the pair of fluctuation segments 65a and 65b fluctuate in opposite directions.
Since the alternate velocity is always maintained by the control circuit unit 63 (to be described later) to have a predetermined amplitude, and the concentrated masses do not change, the Coriolis' force Fc changes in proportion to the input angular velocity.
The fluctuation segments 65a and 65b are distorted by the Coriolis' forces Fc, and the distortions are detected by third piezoelectric conversion elements 612a and 612b which are fixed to detect the distortion directions of the fluctuation segments 65a and 65b. The outputs from the elements 612a and 612b are processed by the control circuit unit 63, thus obtaining an angular velocity.
Terminal outputs from the second and third piezoelectric conversion elements 67, and 612a and 612b are grounded at resistors 613 and 614, and are then input to non-inverting amplifiers 615 and 616, thereby generating amplified detected voltages.
A phase shifter circuit 617 generates a phase-shifted voltage by shifting the phase of the amplified detected voltage by 90.degree. in response to the amplified detected voltage from the non-inverting amplifier 615. The role of the phase shifter circuit 617 will be described below.
The fluctuation mechanism 64 fluctuates in response to a fluctuation application signal input to the first piezoelectric conversion element 66. The most efficient fluctuation amplitude with respect to the fluctuation application signal is obtained at the resonance frequency of the fluctuation mechanism 64. However, in the resonance state, the phase of an actual fluctuation is delayed by 90.degree. from that of the fluctuation application signal input to the first piezoelectric conversion element 66. For this reason, the phase of the amplified detected voltage from the non-inverting amplifier 615 via the second piezoelectric conversion element 67 is delayed by 90.degree. from that of the fluctuation application signal, and is advanced by 90.degree. by the phase shifter circuit 617 to be in phase with that of the fluctuation application signal.
When the in-phase signal is input to the first piezoelectric conversion element 66 to constitute a so-called positive feedback circuit, and the amplified detected voltage from the non-inverting amplifier 615 is increased to be higher than an input signal voltage, the fluctuation mechanism 64 begins to fluctuate.
A rectification circuit 619 generates a rectified voltage by rectifying the phase-shifted voltage in response to the phase-shifted voltage from the phase shifter circuit 617. A fiducial signal generator 620 generates a fiducial voltage for controlling the fluctuation application signal to the first piezoelectric conversion element 66 so as to obtain a constant amplified detected signal from the non-inverting amplifier 615.
A differential amplifier 621 generates a differentially amplified voltage by amplifying the difference between the rectified voltage from the rectification circuit 619 and the fiducial voltage from the fiducial signal generator 620. A multiple circuit 622 multiplies the differentially amplified voltage from the differential amplifier 621 with the phase-shifted voltage from the phase shifter circuit 617, and outputs the product as a feedback voltage corresponding to the fluctuation application signal to the first piezoelectric element 66.
As described above, when the amplified detected voltage from the non-inverting amplifier 615 is set to be higher than the fluctuation application signal voltage, the fluctuation mechanism 64 begins to fluctuate. In this state, however, since the fluctuation gradually increases, and is finally limited by a power supply voltage, an unstable fluctuation with a distorted waveform is obtained.
However, when the amplified detected voltage from the non-inverting amplifier 615 is rectified by the rectification circuit 619, and the difference between the rectified voltage and the fiducial voltage from the fiducial signal generator 620 is multiplied in positive feedback, the product from the multiple circuit 622 decreases as the fluctuation increases and the rectified voltage increases to be close to the fiducial voltage. As a result, the ratio between the fluctuation application signal voltage and the amplified voltage from the non-inverting amplifier 615 decreases. More specifically, the gain of the positive feedback circuit is controlled by the fluctuation amplitude and the fiducial signal, and the fluctuation mechanism 64 stably fluctuates at a constant amplitude.
The output from the non-inverting amplifier 616 is input to a band-pass circuit 623 which allows only a fluctuation frequency component to pass therethrough, thereby removing a disturbance signal (for example, an acceleration signal obtained when the fluctuation segments 65a and 65b are distorted by a gravitational acceleration, and the distortions are detected by the third piezoelectric conversion elements 612a and 612b) in a frequency range considerably lower than the fluctuation frequency.
A synchronous detecter circuit 624 synchronously detects the band-pass amplified detected voltage from the band-pass circuit 623 in response to and in association with the phase-shifted voltage from the phase shifter circuit 617, and generates the synchronously detected result as a synchronously detected voltage.
FIG. 37A is a graph for explaining a synchronous detection state. As indicated by an alternate long and short dashed curve 626, the phase of the alternate velocity advances by 90.degree. from that of a fluctuation 625 of the fluctuation mechanism portion 64 indicated by a solid curve.
The outputs from the third piezoelectric conversion elements 612a and 612b upon application of the angular velocity .OMEGA. are in phase with the alternate velocity, as indicated by an alternate long and two short dashed curve 627. A broken curve represents an output 628 from the second piezoelectric conversion element 67 for detecting a fluctuation of the fluctuation mechanism portion 64, and the outputs from the third piezoelectric conversion elements 612a and 612b are synchronously detected by a phase-shifted voltage obtained by advancing the output 628 by 90.degree. by the phase shifter circuit 617.
FIG. 37B shows the obtained synchronously detected voltage. An angular velocity voltage representing the angular velocity .OMEGA. is obtained by integrating hatched areas by a smoothing circuit 629.
A hand vibration amount (hand vibration angular displacement) can be obtained by integrating the obtained angular velocity output by a known analog or digital integral circuit.
FIG. 38 is an exploded perspective view showing the structure of a correction optical means suitably used for the above-mentioned object.
A bearing 73y is press-fitted in a support frame 72 to which a lens 71 is caulked. A support shaft 74y is supported by the bearing 73y to be slidable in the axial direction. A recess portion 74ya of the support shaft 74y is locked with to pawls 75a of a support arm 75. A bearing 73p is press-fitted in the support arm 75 as well, and a support shaft 74p is supported by the bearing 73p to be slidable in the axial direction.
Note that FIG. 38 also illustrates a rear view of the support arm 75, and a partial front view for clearly showing the pawls 75a.
Light-emitting elements 76p and 76y such as IREDs are adhered to light-emitting element mounting holes 72pa and 72ya of the support frame 72, and their terminals are soldered to lids 77p and 77y (adhered to the support frame 72) which also serve as adhesive boards. The support frame 72 has slits 72pb and 72yb, and light beams emitted from the light-emitting elements 76p and 76y are incident on PSDs 78p and 78y (to be described later) via the slits 72pb and 72yb. Coils 79p and 79y are also adhered to the support frame 72, and their terminals are soldered to the lids 77p and 77y.
Support balls 711 are fitted (at three positions) in a lens barrel 710, which has a pawl portion 710a to which a recess portion 74pa of the support shaft 74p is locked.
Yokes 712p.sub.1, 712p.sub.2, and 712p.sub.3, and magnets 713p are stacked and adhered to each other, and similarly, yokes 712y.sub.1, 712y.sub.2, and 712y.sub.3, and magnets 713y are stacked and adhered to each other. Note that the magnets are arranged to have polarities indicated by arrows 713pa and 713ya.
The yokes 712p.sub.2 and 712y.sub.2 are respectively fixed by screws to recess portions 710pb and 710yb of the lens barrel 710.
Position detection elements 78p and 78y such as PSDs are adhered to sensor bases 714p and 714y (714y is not shown), and are respectively covered by sensor masks 715p and 715y. The terminals of the position detection elements 78p and 78y are soldered to a flexible board 716. Projecting portions 714pa and 714ya (714ya is not shown) of the sensor bases 714p and 714y are fitted in mounting holes 710pc and 710yc of the lens barrel 710, and the flexible board 716 is fixed by screws to the lens barrel 710 via a flexible stay 717. Ear portions 716pa and 716ya of the flexible board 716 respectively extend through holes 710pd and 710yd of the lens barrel 710, and are fixed by screws onto the yokes 712p.sub.1 and 712y.sub.1. The coil terminals and the light-emitting element terminals on the lids 77p and 77y are connected to land portions 716pb and 716yb of the ear portions 716pa and 716ya and to polyurethane-coated copper lines (three-stranded lines).
A plunger 719 is fixed by screws to a mechanical lock chassis 718, is fitted in a mechanical lock arm 721 with a charged spring 720, and is rotatably fixed to the mechanical lock chassis 718 by an axial screw 722.
The mechanical lock chassis 718 is fixed by screws to the lens barrel 710, and the terminal of the plunger 719 is soldered to a land portion 716b of the flexible board 716.
Adjustment screws (three screws) 723 with spherical distal ends are screwed in a yoke 712p and the mechanical lock chassis 718 to extend therethrough, and the adjustment screws 723 and the support balls 711 sandwich the sliding surface (a hatched portion 72c) of the support frame 72 therebetween. The adjustment screws 723 are screwed and adjusted to oppose the sliding surface with a small clearance.
A cover 724 is adhered to the lens barrel 710 to cover the above-mentioned correction optical means.
FIG. 39 is a view for explaining driving control of the correction optical means shown in FIG. 38.
When the outputs from the position detection elements 78p and 78y are amplified by amplification circuits 727p and 727y, and the amplified outputs are input to the coils 79p and 79y, the support frame 72 is driven, and the outputs from the position detection elements 78p and 78y change. When the driving directions (polarities) of the coils 79p and 79y are set in directions to decrease the outputs from the position detection elements 78p and 78y (negative feedback), the support frame 72 is stabilized by the driving forces from the coils 79p and 79y at a position where the outputs from the position detection elements 78p and 78y become almost zero. Note that addition circuits 731p and 731y are circuits for adding the outputs from the position detection elements 78p and 78y and external command signals 730p and 730y, compensation circuits 728p and 728y are circuits for more stabilizing a control system, and driving circuits 729p and 729y are circuits for compensating for currents to be applied to the coils 79p and 79y.
When the external command signals 730p and 730y are supplied to the system shown in FIG. 39 via the addition circuits 731p and 731y, the support frame 72 is very faithfully driven by the command signals 730p and 730y.
A technique for controlling the coils by negatively feeding back the position detection outputs like in the control system shown in FIG. 39 is called a position control technique, and when a hand vibration amount is input as the command signals 730p and 730y, the support frame 72 is driven in proportion to the hand vibration amount.
FIG. 40 is a circuit diagram showing in detail the driving control system of the correction optical means shown in FIG. 39. In the following description, only a circuit for a pitch direction 725p will be explained (the same applies to a yaw direction 725y).
Current-voltage conversion amplifiers 727a and 727b convert photocurrents 727i.sub.1 and 727i.sub.2 generated in the position detection element 78p (comprising resistors R1 and R2) by light emitted from the light-emitting element 76p into voltages. A differential amplifier 727c obtains a difference (an output proportional to the position, in the pitch direction 725p, of the support frame 72) between the outputs from the current-voltage conversion amplifiers 727a and 727b. The current-voltage conversion amplifiers 727a and 727b, the differential amplifier 727c, and resistors R3 to R10 constitute the amplification circuit 727p shown in FIG. 39.
A command amplifier 731a adds the external command signal 730p to the difference signal from the differential amplifier 727c, and constitutes the addition circuit 731p in FIG. 39 together with resistors R11 to R14.
Resistors R15 and R16, and a capacitor C1 constitute a known phase advance circuit, which corresponds to the compensation circuit 728p in FIG. 39.
The output from the addition circuit 731p is input to a driving amplifier 729a via the compensation circuit 728p. The driving amplifier 729a generates a driving signal for the pitch coil 79p, and the correction optical means is displaced. The driving amplifier 729a, a resistor R17, and transistors TR1 and TR2 constitute the driving circuit 729p in FIG. 39.
An addition amplifier 732a calculates a sum (a total sum of light-receiving amounts of the position detection element 78p) of the outputs from the current-voltage conversion amplifiers 727a and 727b, and, hence, a driving amplifier 732b, which receives the sum signal, drives the light-emitting element 76p. The addition amplifier 732a, the driving amplifier 732b, resistors R18 to R22, and a capacitor C2 constitute a driving circuit (not shown in FIG. 39) for the light-emitting element 76p.
The light-emitting amount of the light-emitting element 76p changes very unstably depending on, e.g., the temperature, and the position sensitivity of the differential amplifier 727c changes accordingly. However, when the light-emitting element 76p is controlled by the above-mentioned driving circuit to make the total sum of the light-receiving amounts constant, a change in position sensitivity can be prevented.
In the above-mentioned fluctuation prevention system, a drawback common to the angular displacement detection means, the angular acceleration sensor, and the vibration gyro to be used as the fluctuation sensor (fluctuation detection means) is susceptibility to a disturbance shock fluctuation input. This drawback will be described below.
1) When Angular Displacement Detection Means is Used
The float 53 shown in FIG. 29 is supported by the pivot shafts 512 and the pivot bearings 56, and a small clearance is assured between each pair of the pivot shafts 512 and the pivot bearings 56, so that the float 53 can rotate in a resistance-free state with respect to the base plate 51.
Due to this clearance, the float 53 clutters, and when a shock fluctuation is input, the angular displacement output includes an error corresponding to cluttering of the float 53.
A time required until the cluttering converges is closely related to the time constant of the angular displacement detection means.
The time constant of the angular displacement detection means will be described below.
The float 53 has a nature to return to its original position (a zero output position of the position detection element 59) by the spring force of the winding coil 514. When the spring force is very weak, a time required until the float 53 returns to its original position is prolonged, and this state is referred to as "the angular displacement detection means with a large time constant". Conversely, a state wherein the spring force is strong, and a time required until the float 53 returns to its original position is short is referred to as "the angular displacement detection means with a small time constant".
FIGS. 41A and 41B are board graphs showing the ratio of the relative displacement between the base plate 51 and the float 53 with respect to the fluctuation input to the base plate 51 (the output from the position detection element 59) as a function of the input fluctuation frequency. FIG. 41A is a board graph when the time constant is large (the spring force is weak), and FIG. 41B is a board graph when the time constant is small (the spring force is strong).
When the time constant is large, as shown in FIG. 41A, the ratio of the output from the position detection element 59 to the input fluctuation is flat within a hand vibration (frequency) band, and a hand vibration can be detected with high precision. However, since the spring force is weak, the time required until the cluttering converges is prolonged.
When the time constant is decreased (the spring force is increased), the cluttering converges earlier, but detection precision at the low-frequency side (the lower frequency side than f.sub.02) of the hand vibration band is impaired, as shown in FIG. 41B.
Note that the time constant can be increased/decreased by adjusting the circuit shown in FIG. 32. For example, in FIG. 32, when the resistance of the resistor 519a is increased, and the resistance of the resistor 519b is decreased, the spring force is decreased (the time constant is increased); conversely, when the resistance of the resistor 519a is decreased, and the resistance of the resistor 519b is increased, the spring force is decreased (the time constant is increased).
As described above, when a large time constant (weak spring force) is set to improve hand vibration detection precision, the time required until the cluttering converges is prolonged. For example, when a shock fluctuation is input before exposure onto a film, and exposure is performed before cluttering converges (a hand vibration detection state with poor precision), the correction optical means is driven by an error output component corresponding to the cluttering as well, and a good picture cannot be obtained.
2) When Angular Acceleration Sensor is Used
In the servo angular acceleration sensor shown in FIG. 33, the seesaw 528 is supported by the bearings 525a and 525b, and a shaft. In this case, a frictional force between these components poses the following problem.
When a shock fluctuation is input, the seesaw 528 swings largely. As described above, when the seesaw 528 is rotated, an adjusted control current is generated to return the seesaw 528 to the initial position. In this case, the seesaw 528 cannot be perfectly returned to an initial state due to the frictional force of the bearings 525a and 525b.
When a normal hand vibration angular acceleration is input, the rotational displacement of the seesaw 528 caused by this acceleration is very small, and the frictional force is negligible. However, when the seesaw 528 swings largely like in the input state of a shock fluctuation, the influence of the frictional force cannot be ignored.
An actual phenomenon will be described below. In a normal state, hand vibration angular acceleration detection of .+-.1 V is performed to have the output=0 V of the angular acceleration sensor as the center. However, after a shock fluctuation is input, hand vibration angular acceleration detection is performed to have +5 mV as the center. More specifically, a constant DC bias voltage of 5 mV is superposed on the hand vibration angular acceleration detection.
As described above, the output from the angular acceleration sensor is second-order-integrated by a second-order integral circuit to obtain a hand vibration amount (hand vibration angular displacement). However, when the sensor output is kept integrated including an error, this results in a large hand vibration angular displacement error even if the error is as small as 5 mV. In order to avoid this problem, a known DC cut filter is inserted between the output from the angular acceleration sensor and the integral circuit to cut a DC component (5 mV) from the output from the angular acceleration sensor, and thereafter, the output is integrated.
The DC cut filter may cut not only a DC component but also a hand vibration frequency band if its time constant is small, as in the above-mentioned angular displacement detection means. For this reason, the time constant of the DC cut filter must be set to be large. However, when the time constant is set to be large, the time required for cutting a DC component is prolonged.
FIG. 42A is a board graph showing the characteristic of the DC cut filter with a large time constant. In FIG. 42A, the frequency of an input signal (an output from an angular accelerometer) is plotted along the abscissa, and the gain (attenuation factor) of the input signal by the DC cut filter is plotted along the ordinate.
As can be seen from FIG. 42A, the DC cut filter has a characteristic of attenuating frequency components, below a frequency f.sub.0, of the input signal.
In the characteristic shown in FIG. 42A, since the DC cut filter does not attenuate frequency components in a hand vibration frequency band, it functions as a satisfactory DC cut filter (which can cut frequency components below the frequency f.sub.0), but requires a long time until a DC component is cut. This is because if f.sub.0 in FIG. 42A is set to be 0.1 Hz, the DC cut filter cuts signal components from a DC component to 0.1 Hz. In this case, in order to sufficiently cut a component of 0.1 Hz, 10 seconds (wavelength: 10 seconds) are required
In order to shorten the DC cut time, when a small time constant is set, as shown in FIG. 42B, the DC cut filter cuts frequency components below a frequency fl. In this case, if f.sub.1 &gt;f.sub.0, and f.sub.1 is set to be 5 Hz, a DC component can be cut in 0.2 seconds. However, since the filter undesirably cuts components from a DC component to a component of 5 Hz, low-frequency components of a signal in a hand vibration frequency range (1 to 12 Hz) are also attenuated, thus disturbing hand vibration detection with high precision.
Therefore, since the DC cut filter with a large time constant, which requires a long time until a DC component is cut, is used, if a shock fluctuation is input before exposure, and exposure is performed before a DC variation caused by the fluctuation is sufficiently removed, the correction optical means is driven by a signal including an error. As a result, a good photographing operation cannot be performed.
FIG. 43A is a board graph of the second-order integral circuit used in the angular acceleration sensor. This circuit has a characteristic of integrating frequency components, higher than a frequency f.sub.0, of an input signal. FIG. 43B is a board graph obtained when the time constant of the integral circuit is decreased to attain a characteristic of integrating frequency components higher than a frequency f.sub.1 (f.sub.1 &gt;f.sub.0). In FIG. 43B, the gain (the amplification factor of an input signal) at the lower frequency side than the frequency f.sub.1 becomes smaller than that of the characteristic in FIG. 43A (which is also illustrated by an alternate long and shot dashed line in FIG. 43B). This indicates that a low-frequency error (e.g., a DC component) can be reduced. However, since a hand vibration band cannot be sufficiently integrated by the characteristic shown in FIG. 43B, hand vibration detection with high precision cannot be realized.
Therefore, the integral circuit having the characteristic in FIG. 43A with a large time constant must be used although low-frequency errors cannot be reduced.
Note that the time constant of the fluctuation sensor when the angular acceleration sensor is used represents the time constants of the DC cut filter and the integral circuit.
3) When Vibration Gyro is Used
In FIG. 36, if the fluctuation driving portion 64 and the fluctuation segments 65a and 65b are mounted with high orthogonality, the fluctuation segments 65a and 65b fluctuate in only the directions of the arrows 68a and 68b. However, if the mounting orthogonality is poor, the fluctuation segments 65a and 65b begin to fluctuate in the directions of arrows 611a and 611b or in directions opposite thereto.
If a given fluctuation is generated in the directions of the arrows 611a and 611b, a given angular velocity (DC output) is undesirably detected even when no angular velocity is input.
In order to cut such a DC output, the output from the vibration gyro (to be referred to as an angular velocity sensor hereinafter) is filtered through a DC cut filter, and thereafter, a hand vibration angular displacement is calculated.
FIG. 44A is a board graph of a DC cut filter with a large time constant. In FIG. 44A, the abscissa represents the frequency of an input signal, and the ordinate represents the attenuation of the input signal (output from the angular velocity sensor) by the DC cut filter.
As can be seen from FIG. 44A, the DC cut filter attenuates low frequency components below a frequency f.sub.0, and the band components from a DC component to f.sub.0 of the output from the angular velocity sensor is cut by the DC cut filter. More specifically, a given angular velocity, which causes an error, is cut, and a hand vibration frequency band is not attenuated. However, the DC cut filter with the above-mentioned characteristic requires a long time until a DC component is cut. This is because if a DC component is to be cut without influencing the hand vibration frequency band (1 to 12 Hz), f.sub.0 must be set near 0.1 Hz, and in order to sufficiently cut a signal component of 0.1 Hz, 10 seconds as a reciprocal number (wavelength) of the frequency are required.
Thus, when f.sub.0 is set at the high frequency side to attain a characteristic with a small time constant, as shown in FIG. 44B (f.sub.1 =2 Hz), only 0.5 seconds are required until a DC component is cut, but the hand vibration band is also attenuated, thus deteriorating image blur prevention precision.
A DC cut filter with a large time constant must be used. For example, if a shock fluctuation is input before exposure, the fluctuation mechanism 61 is slightly distorted by this shock, and the fluctuation amount of the vibration segments 65a and 65b in the directions of the arrows 611a and 611b by the fluctuation driving portion 64 (leak fluctuation) changes. For this reason, a DC component also changes, and as a result, a long time is required to remove the DC component.
Therefore, if exposure is performed before removal of the DC component, a satisfactory photographing operation is cannot be performed.
FIG. 45A is a board graph showing the characteristic of an integral circuit for integrating the output from a DC cut filter. The integral circuit has a characteristic of integrating frequency components above a frequency f.sub.0. FIG. 45B is a board graph when the time constant of the integral circuit is decreased to attain a characteristic of integrating frequency components higher than a frequency f.sub.1 (f.sub.1 &gt;f.sub.0). In FIG. 45B, the gain (amplification factor of an input signal) at the lower frequency side than the frequency f.sub.1 becomes smaller than that of the characteristic (also illustrated in FIG. 45B by an alternate long and short dashed line) in FIG. 45A. This indicates that a low-frequency error (e.g., a DC component) is reduced. However, since the hand vibration frequency band cannot be sufficiently integrated by the characteristic shown in FIG. 45B, hand vibration detection with high precision cannot be realized.
Therefore, the integral circuit having the characteristic in FIG. 45B with a large time constant must be used although a low-frequency error cannot be reduced.
Note that the time constant of the fluctuation sensor when the angular velocity sensor is used represents the time constants of the DC cut filter and the integral circuit.